1. Field of the Invention
The present invention relates to an antenna with a built-in filter and to an electronic device.
2. Description of Related Art
Heretofore, an electronic device such as a handy terminal and a personal digital assistant (PDA), which has a wireless communication function, has been known. An antenna for wireless communication is mounted on this electronic device.
In some case, the antenna unnecessarily radiates a wave at an unintended frequency depending on a design of a transmission unit for the wireless communication. In order to solve this problem, it is necessary to eliminate such transmission of the unnecessary frequency by changing structures of a transmission circuit and the electronic device. However, it has been difficult to perform such a change for the already fabricated and completed electronic device.
An antenna with a built-in filter has been known, in which, in order to prevent the transmission of the unnecessary frequency, a filter is formed in a stacked dielectric structure to which a radiation element is connected (for example, refer to Japanese Patent Laid-Open Publication No. 2004-40579 and International Publication No. 2002/067379). By this filter, an unnecessary frequency component of a transmission signal is attenuated.
However, when the conventional antenna with the built-in filter is implemented in a small cabinet, the ground and an antenna element come close to each other, a capacitance component therebetween is increased, and it has been apprehended that impedance may be consequently lowered.